Proposed by Lord President Rassilon as the last resort to winning the Last Great Time War, the Ultimate Sanction involved the creation of a paradox so severe that the resulting spatial-temporal rupture would rip the Time Vortex apart.
As this would be a suicidal measure, Rassilon devised a way of allowing the Time Lords to escape the disintegration of Creation by having the whole race shed their corporeal bodies and become creatures of consciousness alone, ones that would escape the effects of time and of cause and effect. (TV: The End of Time)
This plan was thwarted when the Doctor came into possession of the Moment and used it to destroy almost every participant of the Last Great Time War (TV: The End of Time) and time lock the Time War itself. (TV: The Stolen Earth)
Nevertheless, Rassilon nearly succeeded when his sleeper agent, the Saxon Master, used a Whitepoint Star diamond to send a physical rhythmic signal of four beats into time and space. Rassilon locked onto that signal. He used it as a homing beacon to break Gallifrey and every participant of the Last Great Time War out of the time lock and begin the End of Time.
Rassilon's plan was again foiled when the Tenth Doctor used Wilfred Mott's old service revolver to destroy the diamond. Rassilon tried to kill the Doctor for this, but was attacked by the Master, saving the Doctor. The Master assaulted the Time Lords as Gallifrey was plunged back into its last day. (TV: The End of Time)
This event was foreseen by the Ood (TV: Planet of the Ood), Carmen (TV: Planet of the Dead), the Trickster (TV: The Wedding of Sarah Jane Smith) and apparently even Lord Azlok of the Viperox. (TV: Dreamland) They all tried to warn the Doctor through prophecies, which also informed him of his upcoming regeneration.
News of the Ultimate Sanction, or at least that the High Council was planning something, was brought to the General by Androgar, but the General dismissed the Council's plans as having "already failed". (TV: The Day of the Doctor)
Behind the scenes
- Rassilon planned for the Time Lords to escape the effects of the Ultimate Sanction by becoming "creatures of pure consciousness". This is exactly what the Celestial Intervention Agency did in the aborted timeline of the War, becoming the Celestis. (PROSE: Alien Bodies)